Is it fair for someone who calls themselves a “seed” investor to require traction?

It’s completely fair. If you’re building a web-based startup these days, you should be able to demonstrate initial traction on an idea with very little up-front investment—a couple of months of your time and a few hundred dollars in hosting costs, perhaps. Being able to do that is an excellent indicator that you’re a good bet for a seed investor. If you are unable to do that, you’re a much higher risk for investment.

Remember: you’re competing for investment with many other startups. If they’ve managed to demonstrate traction using limited resources and you haven’t, you’ll find it a lot harder to raise money compared to them.